Impregnating nonwovens with latexes of a butadiene polymer and a carboxyl polymer

ABSTRACT

A PROCESS FOR OBTAINING NONWOVEN MATERIALS HAVING IMPROVED PHSICAL PROPERTIES, ESPECIALLY INTERNAL BOND STRENGTH AND RESISTANCE TO DELAMINATION IS PROVIDED. NONWOVEN FABRICS AND PAPERS IMPREGNATED WITH CARBOXYLCONTAINING BUTADIENE POLYMER LATICES, CONTACING A CARBOXYL-CONTAINING POLYMER, ARE EXPOSED TO AMMONIA OR AMINE VAPORS PRIOR TO THE DRYING AND CURING OPERATIONS TO OBTAIN THE IMPROVED PROPERTIES. PAPERS TREATED IN THIS MANNER HAVE SHOWN A MARKED INCREASE IN INTERNAL BOND STRENGTH.

United States Patent US. Cl. 11762.2 11 Claims ABSTRACT OF THE DISCLOSURE A process for obtaining nonwoven materials having improved physical properties, especially internal bond strength and resistance to delamination is provided. Nonwoven fabrics and papers impregnated with carboxylcontaining butadiene polymer latices, containing a carboxyl-containing polymer, are exposed to ammonia or amine vapors prior to the drying and curing operations to obtain the improved properties. Papers treated in this manner have shown a marked increase in internal bond strength.

CROSS REFERENCE TO RELATED APPLICATION This is a continuation-in-part of my copending application Ser. No. 739,584, filed May 20, 1968, now abandoned.

BACKGROUND OF THE INVENTION Polymer latices have been used for many years for coating and impregnating papers and more recently in the manufacture of nonwoven fabrics. Typically, the paper or nonwoven is saturated with the latex and then the water removed leaving the polymer behind to bond the fibers in the finished nonwoven. Aside from the type of binder employed, one of the more important factors governing the ultimate physical properties achievable with a nonwoven is the amount of binder present in the nonwoven and also the uniformity with which the binder is dispersed throughout the substrate. If the nonwoven on a whole is deficient in bonding agent or if localized areas are deficient, the physical properties of the nonwoven, especially the internal bond strength and the resistance to delamination, are quite low and often the nonwoven is rendered unsuitable for many applications.

The problem of obtaining adequate and uniform binder throughout the nonwoven material is especially significant when using the latex binder systems. With these latex systems it is sometimes so diflicult to incorporate suflicient binder to obtain the desired level of physical properties that it becomes necessary to resaturate the nonwoven with the latex a second time after drying the first binder solution. This, however, is a time-consuming and costly operation and therefore not generally desirable.

Efforts to overcome the problem of achieving an ac ceptable binder content has led to much 'work primarily in the field of developing improved latex binder systems.

Typically, the improved latex binder systems developed to date contain monomers capable of reacting upon the application of heat, chemical reagents or catalysis to form cross-linked polymers having improved physical properties. This approach is not completely satisfactory, however, since the binders, even though more eflicient, are susceptible to migration through the nonwoven material. This migration occurs during the drying or curing of the nonwoven. As the water is removed the polymeric binder is carried toward the surface of the nonwoven material creating a nonuniform distribution of the binder throughout the nonwoven and consequently poor physical properties.

3,822,143 Patented July 2, 1974 The viscosity of the binder latex can be increased prior to saturation of the nonwoven by the addition of thickening agents such as natural gums and pastes, polyvinyl alcohol and the like. This technique, however, is only partially effective to reduce the migration within the nonwoven material since it creates the additional problem of achieving uniform initial saturation of the nonwoven due to the poor penetrability and the difliculty of application of the thickened latices.

Butadiene-based polymer latices, especially butadieneacrylonitrile and butadiene-styrene latices, are an important class of binders for use with papers and nonwoven fabrics. They provide nonwoven fabrics having an acceptable balance of physical properties and wear endurance. The butadieneacrylonitrile copolymer latices are especially important for nonwoven applications since they provide nonwovens having good fiber adhesion, superior aging and resistance to oils.

SUMMARY OF THE INVENTION I have now developed a process whereby nonwoven materials having markedly improved internal bond strength or resistance to delamination are obtained when the nonwoven is saturated with a butadiene polymer anionic latex containing a carboxyl-containing polymer and then exposed to ammonia or amine vapors prior to drying or curing. To obtain these improved properties the nonwoven web or mat is impregnated with the butadiene polymer latex which for the purposes of the present invention is obtained by blending a carboxyl-containing polymer or copolymer latex with the butadiene polymer latex.

The nonwoven materials treated in accordance with the present process have improved internal bond strength or resistance to delamination over nonwoven prepared conventionally, that is, without the ammonia or amine exposure. The present process is equally applicable to both fabrics and papers. It provides a means for achieving a more uniform distribution of the polymeric binder within the finished nonwoven as a result of the in situ thickening of the latex binder prior to the drying step. This in situ thickening reduces the migration of the polymer toward the surface of the nonwoven as the water is removed after a uniform initial saturation has been obtained.

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DETAILED DESCRIPTION The process of the present invention is applicable to any nonwoven material, that is, the particular fiber used in the make-up of the nonwoven and the thickness of the nonwoven does not limit the application of the present process. This is not to say that certain fibers are not more useful with the butadiene binder latices for certain nonwoven applications than others, but only that if a fiber has the required specifications to be formed into a nonwoven web or mat then the nonwoven so formed may be treated according to the present process.

Natural fibers such as cotton, wool, silk, sisal, cantala, henequen, hemp, jute, kenaf, soon and ramie may be used to form the nonwoven web or mat as well as synthetic fibers or filaments. Useful synthetic fibers include: rayon (viscouse); cellulose esters such as cellulose acetate and cellulose triacetate; proteinaceous fibers such as those manufactured from casein; polyamides (nylons) such as those derived from the condensation of adipic acid and hexamethylenediamine or the selfcondensation of caprolactam; polyesters such as polyethylene glyocol terephthalte; acrylic fibers containing a minimum of about acrylonitrile with vinyl chloride, vinyl acetate, vinyl pyridine, methacrylonitrile or the like and the so-called modacrylic fibers containing smaller amounts of acrylonitrile; fibers of copolymers of vinyl chloride with vinyl acetate or vinylidene chloride; fibers obtained from the formal derivatives of polyvinyl alcohol; olefin fibers such as polyethylene and polypropylene; and the like.

The process of the present invention is particularly advantageous for use with specialty papers which require specific binders in order to modify the structural properties of the paper. Papers obtained from bleached or nonbleached pulp may be employed; also, those obtained by the unbleached sulfite, bleached sulfite, unbleached sulfate (kraft), semi-bleached and bleached sulfate processes. Papers prepared wholly from synthetic fibers and those obtained from blends of natural cellulose and synthetic fibers also may be used.

The nonwoven mat or web may be formed by conventional techniques. For example, for papers they will be formed on a moving fine wire screen from an aqueous suspension of the fibers. When other fibers are to be formed into a nonwoven, depending on the particular fiber or fiber blend being used, whether the fibers are to be orientated or deposited at random, the thickness of the nonwoven, etc., the fibrous web can be formed by carding, garnetting, deposition from an air stream, deposition from solution, deposition from a melt, wet-laying, or the like.

The latex binders employed for the process of the present invention are butadiene-based polymer latices. The required carboxyl functionality is provided by a carboxylcontaining polymer blended with the butadiene polymer latex. The carboxyl group present in the butadiene latex will constitute from about 0.5 to about 25% by weight based on the total polymer.

The butadiene polymer latices useful in the present invention are obtained by polymerizing from about 29.5 to 100% by weight butadiene preferably with up to about 70% by weight styrene or up to about 50% by weight acrylonitrile. In addition to these monomers, up to about 40% by weight one or more other polymerizable comonomers may be interpolymerized therewith. Typically, these polymerizable comonomers will be vinylidene monomers having at least one terminal CH group and being free of amine groups. Polymerizable comonomers useful in the present invention include: other vinyl aromatics as a-methyl styrene, chlorostyrene, vinyl naphthalene; a-olefins such as ethylene, propylene and isobutylene; vinyl halides such as vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, and vinylidene fluoride; vinyl esters such as vinyl acetate, other at, fl-olefinically unsaturated nitriles as methacrylonitrile; alkyl vinyl ethers such as methyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isopropyl vinyl ether and haloalkyl vinyl ethers as 2-chloroethyl vinyl ether; esters of a, 3-olefinically unsaturated carboxylic acids such as methyl acrylate, ethyl acrylate, the propyl acrylates, the butyl acrylates, the amyl acrylates, cyclohexyl acrylate, 2- methyl hexyl acrylate, n-octyl acrylate, 2-ethyl hexyl acrylate, methyl methacrylate, ethyl methacrylate, noctyl methacrylate, dodecyl methacrylate, methyl ethacrylate, ethyl ethacrylate and the like; haloalkyl acrylates as chloropropyl acrylates but excluding aminoacrylates and methacrylates; vinyl pyridine; a,,B-olefinically unsaturated amides such as acrylamide, N-methyl acrylamide, N-t-butyl acrylamide, N-cyclohexyl acrylamide, diacetone acrylamide, methacrylamide, and N-ethyl methacrylamide; a,B-olefinically unsaturated N-alkylol amides having the structural formula wherein R is a hydrogen or an alkyl group containing from 1 to 4 carbon atoms and x is a number from 1 to 4, such as N-methylol acrylamide, N-ethanol acrylamide, N-propanol acrylamide, N-methylol methacrylamide, and N-ethylol methacrylamide; poly-functional compounds such as methylene-bisacrylamide, ethylene glycol dimethacrylate, diethylene glycol diacrylate, allyl pentaerythritol and divinyl benzene; one or more a,fl-olefinically unsaturated carboxylic acid monomers containing from 3 to 10 carbon atoms such as acrylic acid, methacrylic acid, ethacrylic acid, a-chloroacrylic acid, a-cyanoacrylic acid, crotonic acid, fi-acryloxy propionic acid, hydrosorbic acid, sorbic acid, a-chlorosorbic acid, cinnamic acid, p-styrylacrylic acid, itaconic acid, citraconic acid, maleic acid, fumaric acid, mesaconic acid, gluatconic acid, aconitic acid and the like. The preferred acid monomers are the a,,B-monoolefinically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid. Mixtures of one or more of the above-mentioned carboxylic monomers may be employed if desired. The styrene and acrylonitrile may be present individually or in combination in the butadiene latices. Useful nonwovens have been obtained when the butadiene latex contained about equal parts of styrene and acrylonitrile interpolymerized; and the like as known to those skilled in the art.

The butadiene polymer latices may be prepared using any of the conventional emulsion polymerization techniques. The aqueous medium may contain a surface active agent. When an emulsifier or dispersing agent is used to prepare the polybutadiene binders it may range from about 0.1, as 0.5, up to about 6% or more, as 10%, by weight based on the total monomers. The emulsifier may be charged at the outset of the polymerization or may be added incrementally or by proportioning throughout the run. Any of the general types of anionic or nonionic emulsifiers may be employed, however, best results are obtained when anionic emulsifiers are used. Typical anionic emulsifiers which may be used include those types known to those skilled in the art, for example, as disclosed beginning Page 102 in J. Van Alphens Rubber Chemicals, Elsevier, 1956, for example, the alkali metal or ammonium salts of the sulfates of alcohols containinng from 8 to 18 carbon atoms such as, for example, sodium lauryl sulfate, ethanol amine lauryl sulfate and ethyl amine lauryl sulfate; alkali metal and ammonium salts of sulfonated petroleum or paraflin oils; sodium salts of aromatic sulfonic acids such as dodecane-l-sulfonic acid and octadiene-l-sulfonic acid; aralkyl sulfonates such as sodium isopropyl benzene sulfonate and sodium dodecyl benzene sulfonate; alkali metal and ammonium salts of sulfonated dicarboxylic acid esters such as sodium dioctyl sulfosuccinate and disodium N-octadecyl sulfosuccinamate; alkali metal or ammonium salts of the free acids of complex organic monoand diphosphate esters; and the like. So-called nonionic emulsifiers are octylor nonylphenyl polyethoxyethanol and the like. Preferred as emulsifiers are the alkali metal salts of the aromatic sulfonic acids and the sodium salts of the aralkyl sulfonates of the formula wherein R is alkyl or alkenyl having 8 to 20 carbon atoms such as octyl, decyl, dodecyl, alkoxy or ethoxy groups, or aryl, such as phenyl radical of the formula wherein R' is H or an aliphatic radical containing 1 to 16 carbon atoms as the butyl, decyl, dodecyl and like alkyl or alkenyl radicals, y is CH or O, and naphthyl erization emulsifiers and stabilizers to the polymeric latex binders in order to improve the latex stability if it is to be stored for prolonged periods prior to use. Such postpolymerization emulsifiers may be the same as, or different than, the emulsifier employed in conducting the polymerization, preferably anionic or nonionic surface active agents.

To initiate the polymerization free radical catalysts are employed. The use of such catalysts, although in certain systems not absolutely essential, insure a more uniform and controllable polymerization and a satisfactorry polymerization rate. Commonly used free radical initiators include the various peroxygen compounds such as the persulfates, benzoyl peroxide, t-butyl hydroperoxide, l-hydroxycyclohexyl hydroperoxide; azo compounds such as azodiisobutyronitrile, and dimethyl azodiisobutyrate; and the like. Especially useful as polymerization initiators are the water-soluble peroxygen compounds such as hydrogen peroxide and the sodium, potassium and ammonium persulfates.

The alkali metal and ammonium persulfate catalysts may be employed by themselves or in activated redox systems. Typical redox systems include the persulfates in combination with: a reducing substance such as a polyhydroxy phenol and an oxidizable sulfur compound such as sodium sulfite or sodium bisulfite, a reducing sugar, a diazomercapto compound, a ferricyanide compound, dimethylaminopropionitrile and the like. Heavy metal ions such as silver, cupric, iron, cobalt, nickel and others may also be used to activate persulfate catalyzed polymerizations. In general the amount of free radical initiator employed will range between about 0.1 to 5% based on the weight of the total monomers. The initiator is generally completely charged at the start of the polymerization, however, incremental addition or proportioning of the initiator throughout the polymerization is often desirable.

In conducting the polymerization for the preparation of the butadiene binder latices of the present invention the monomers are typically charged into the polymerization reactor which contains the water and the emulsifying agent. The reactor and its contents are then heated and the polymerization initiator added. The temperature at which the polymerization is conducted is not critical and may range from about C. to about 80 C. or higher. Excellent results, however, have been obtained when the polymerization temperature is maintained between C. and 60 C. Polymerization modifiers such as the primary, secondary and tertiary mercaptans, buffers, electrolytes and the like may also be included in the polymerization.

The present process is applicable where the butadiene polymer latices themselves contain no carboxyl functionality, where the butadiene latices contain insufficient carboxyl functionality so that they would be ineflective by themselves for use in the present process or where more carboxyl is required than is desired in the butadiene polymer. These latter latices are useful, however, when there is added a water-soluble salt of a copolymer obtained by polymerization of an a,/3-olefinically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, itaconic acid and the like as defined above with one or more esters of an m,fi-olefinically unsaturated carboxylic acid or a copolymer of an u,B-olefinically unsaturated carboxylic acid with a polyalkenyl polyether of a polyhydric alcohol.

Useful copolymer additives of the first type include copolymers readily prepared by those skilled in the art in water as described or in solvents as isopropanol and the like containing from about 15 to 70% by weight of methacrylic acid interpolymerized with about 30 to 85% by weight of an ester of an o fl-olefinically unsaturated carboxylic acid. More preferably, such copolymers will contain about 35 to 65% of the methacrylic acid and about 40 to 65% of an acrylic ester. Up to 50% of the ester may be replaced with one or more amine-free vinylidene monomers as described herein. Acrylic esters suitable for the preparation of these copolymers include those derived from alcohols containing from 1 to 8 carbon atoms such as methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol, t-butanol, hexanol, cyclohexanol and octanol. Preferably the acrylic ester will be derived from one of these above-mentioned alcohols with acrylic or methacrylic acid. When the acrylic ester is ethyl acrylate the copolymer will generally contain about 40 to 55% methacrylic acid. When the acrylic ester is methyl acrylate about 35 to 50% by weight methacrylic acid should be present in the copolymer. Usually the salt will be an alkali metal or ammonium salt. Mixtures of one or more of the acrylic esters may be employed if desired to make up these copolymer additives, ethyl acrylate in combination with methyl methacrylate being especially preferred. The above-mentioned copolymers are particularly effective if they contain about 0.1 to 0.8% by weight of a cross-linking monomer such as methylene-bis-acrylarnide, ethylene glycol dimethacrylate, diethylene glycol diacrylate, allyl pentaerythritol, divinyl benzene or the like.

Also useful as additives for use with the polybutadiene binder latices are polymeric thickeners obtained by the polymerization of an a,fl-olefinically unsaturated carboxylic acid such as acrylic acid, itaconic acid, maleic acid, fumaric acid, or the like, with a polyalkenyl polyether of a polyhydric alcohol, said polyhydric alcohol containing about 4 carbon atoms and at least three hydroxyl groups and said polyether containing more than one alkenyl group per molecule. These thickeners are described in detail in US. Pat. No. 2,798,053 and the disclosure thereof is incorporated herein.

The polymeric thickeners for purposes of the present invention are blended with the butadiene binder latices prior to saturation of the nonwoven. Depending on the carboxyl content of the polymer additive and the desired carboxyl level in the latex hinder, the amount of these additives will vary within wide limits. Generally, the above-described external copolymer thickeners will constitute from about 0.1 to 10% by weight based on the total polymer content of the binder latex and more preferably from about 0.5 to 40% by weight.

The present process consists of exposing the nonwoven material which has been saturated with one of the abovementioned carboxyl-containing polymeric latex binders to the vapors of ammonia or amines. By such exposure, the latex binder is thickened in situ, thereby inhibiting the migration of the polymeric binder from the interior regions of the nonwoven toward the surface as the water is removed during the drying operation. Thus, a more uniform distribution of the polymeric binder throughout the nonwoven than was previously possible is achieved. The net result of such treatment is a noticeable improvement in the physical properties of the nonwoven material. The internal bond strength or delamination resistance and generally the tensile strength, especially the 'wet tensile strength, of the nonwovens are increased by employing the process of the present invention.

To achieve the maximum advantage of this invention, the pH of the polymer latices must be maintained below specific limits during the saturation or impregnation. This insures the complete penetration and uniformity of the binder latex throughout the nonwoven material which is essential to obtain the improved physical properties. Although the pH requirement will vary from one latex to another, depending on the monomers employed and the carboxyl content, to be acceptable for impregnation the pH should preferably be maintained on the acid-side. A neutral or slightly basic latex will give acceptable results in most instances, however. In general, the pH of the carboxyl-containing butadiene polymer latex will be maintained at about 7.5 or below and more preferably between about 6.5 and 2.5. Excellent results are achieved when latices at the higher pH limits are acidified prior to saturation to achieve -a more desirable pH and viscosity. To facilitate the saturation of the nonwoven, the total solids of the latex binder is generally maintained below about 50% and excellent results are obtained with latices containing about 15 to 35% total solids.

A critical feature of the present invention is the exposure of the saturated nonwoven material to ammonia or amine vapors. Although ammonia is generally preferred due to its ready availability, gaseous nature and excellent solubility in the binder latices at the temperatures employed, primary, secondary or tertiary aliphatic monoamines may also be employed to give excellent results. Typical amines which can be used may contain up to 12 carbon atoms, however, amines containing up to 6 carbon atoms are generally preferred. Gaseous amines such as methyl amine, ethyl amine, dimethyl amine and trimethyl amine have produced excellent results. The higher molecular weight amines which are normally liquids at room temperature, such as primary amines containing from 3 to 11 carbon atoms and the lower secondary and tertiary amines, which will normally exert an appreciable vapor pressure at room temperature, or slightly above, and are readily soluble in water may also be employed. Generally, the amines useful in the present process should have boiling points less than about 150 C. and more preferably less than 100 C. The ready solubility of the ammonia and amines in water insures that binder latex even in the innermost regions of the nonwoven will be uniformly acted on, thus rendering in situ thickening of the latex to minimize subsequent binder migration. It is the ability of the ammonia and amines to be instantaneously, or essentially so, taken up by the saturated nonwoven and contact both the interior and surface regions with the same effectiveness, which renders the present process so useful and permits the development of superior physical properties in the nonwovens treated in accordance with the present invention.

Attempts to achieve this uniform treatment of saturated nonwovens using other techniques were unsuccessful. Either the binder could not uniformly penetrate the nonwoven in the cases where thickening of the binder latex prior to saturation was employed, or when post-thickening of the binder latex was attempted with agents other than the ammonia or amines of this invention, the initial thickening occurring at the surface of the nonwoven is so pronounced and so rapid that it impedes further penetration of the thickening agent to the interior regions of the nonwoven and consequently these interior regions are subject to migration of the binder upon drying.

Exposure of the saturated nonwoven material to the ammonia or amine vapors will vary depending on the particular latex binder and thickening agent employed. Contact times will generally be less than about 80 minutes, preferably they will range between about 2 seconds and 5 minutes. With ammonia and the more volatile amines, contact times between 5 seconds and 1 minute have been successfully employed and found to impart maximum properties to the cured nonwoven material. Once maximum thickening of the binder latex is achieved, additional exposure to the ammonia or amines will produce no further improvement in the nonwoven properties. Neither will any detrimental effects be realized from prolonged exposure to the ammonia or amine vapors, however.

Exposure to the ammonia or amine is conveniently brought about in a chamber maintained at room temperature or above, such as a gravity oven, where in a suificient concentration of the ammonia or amine vapors can be maintained for contact with the saturated nonwoven. Although the exposure ovens can be maintained at elevated temperatures, these temperatures should generally not exceed 212 F., particularly if long exposure times are employed. Because of the short contact times possible with the present process, the saturated nonwoven may be continuously passed through the gaseous ammonia or amine to facilitate the exposure step. Such a continuous process would be highly desirable for large-scale commercial operations.

After exposure and thickening with the ammonia or amine, the nonwoven material is then dried and cured. The drying step is normally conducted by passing the nonwoven material through one or more ovens or heating chambers maintained at a temperature between about 200 and 325 F. The preferred drying temperature will be in the range between about 225 and 275 F. The drying ovens may be maintained at subatmospheric pressure to facilitate the removal if so desired. The dried nonwoven is then typically passed through one or more ovens maintained at higher temperatures to effect the cure of the binders employed and develop the ultimate physical characteristics of the nonwoven. Such curing ovens are maintained at temperatures between about 250 and 325 F., preferably between 275 and 300 F. In either the drying operation or the curing step the nonwoven material may be passed through the heating chamber once or it may be recycled for as many times as required. The drying and curing need not be distinct steps, depending on the temperature requirements of the particular binder latex employed.

The following examples will illustrate the invention more fully. They are not'intended to limit its scope however. All parts and percentages set forth in the examples are given on a weight basis unless otherwise indicated.

EXAMPLE I A butadiene polymer latex containing interploymerized can-boxyl functionality was prepared for use as a binder. The latex was prepared by emulsion polymerizing 52 parts butadiene, 45 parts styrene and about 1.5 parts each of acrylic acid and methacrylic acid in 95 parts water containing 3 parts of an alkyl benzene sulfonate emulsifier. The polymerization was initiated with 0.15 part of a potassium persulfate catalyst. The polymerization was maintained at about 50 C. until essentially complete conversion was achieved. The resulting butadiene copolymer latex contained about 50% total solids.

A saturation bath was prepared by diluting the latex obtained to 25% total solids with distilled water. Ten mil uncoated flat paper (Patterson Parchment Company) having a minimum fiber to fiber contact and placed in a Dacron marquisette envelope was then saturated by submerging the paper in the latex bath. The excess binder latex was then removed by passing the paper between padder squeeze rolls maintained at about 20 pounds pressure. The saturated paper was then removed from the marquisette envelope.

The paper saturated in the above manner was then exposed to ammonia vapors for three minutes by placing the papers in warm (60 to C.) gravity oven con-taining ammonia vapors. The ammonia atmosphere was achieved by placing a fresh 20% solution of ammonium hydroxide in a pan on the floor of the oven prior to inserting the papers. Immediately after exposure to the ammonia the papers were dried and cured in a 276 F. air oven for five minutes.

Physical properties of the cured papers were then determined and compared against those obtained with iden- 'tically saturated papers but not exposed to ammonia. Tensile (breaking) strengths of the nonwoven materials were determined in accordance with AS'IM D11'17-63 cut-strip method. Samples used for determining the wet tensile strength were soaked in water at room temperature for 16 hours immediately prior to testing. Resistance to delamination for fibers and internal bond strength for papers was determined by sandwiching a 1 x 6" sample of the nonwoven between two 1% x 6" pieces of Bondex T-7 tape, sealing with the weight of an iron at 275 F. for 30 seconds on a heated plate and peeling the tapes apart at a rate of 12 per minute. The force required to pull the tapes apart is reported in ounces/inch.

Papers saturated with the above-described butadiene binder latex and dried and cured in the conventional manner had a wet breaking strength of 2.1 pounds/inch and an internal bond strength of 14.4 ounces/inch. Identical paper samples exposed to ammonia vapors after satura- 10 more other polymerizable comonomers, are useful for the present process.

I claim:

1. A process for obtaining increased internal bond strength in papers and nonwoven fabrics which comprises:

tion and prior to drying and curing in accordance with (1) impregnating a nonwoven web with a mixture of (A) the process of the present invention had wet breaking an aqueous butadiene copolymer latex, said copolymer strengths of 3.1 pounds/inch and internal bond strength Consisting essentially of (a) from about 29.5 to 100% of 16.5 ounces/inch. by weight of butadiene, (b) from 0 to about 70% by When the above butadiene latex is used to saturate fab- Weight of a styrene or up to about 50% by weight of an rics rather than papers similar improved properties are acrylonitrile, (c) from 0 to about 40% by weight of one obtained. Also, the improved properties of both papers and or more other polymerizable vinylidene comonomers havfabrics saturated with these canboxylated butadiene latices ing at least one terminal CH =C group and being free are improved when exposure times less than three minof amine group, with (B) about 0.5 to about 25.0% by u-tes are used. Exposure times as low as 10 seconds are ight of carboxyl groups provided by a polymer of efiectlve. Exposure to diethylamine instead of ammonia a,B-olefinically unsaturated carboxylic acids containing gives comparable improvement in the wet tensile strength from 3 to 10 carbon atoms in amount of at least 15% by and internal bond strengths, weight with an ester 0f the formula EXAMPLE II CHI=CCOOR| The butadiene latex prepared in Example I was diluted to total solids and the pH adjusted to 3.5 by the addition of 10% acetic acid. 2.5 parts of a water-soluble Q R 18 H 3 and R 18 a hydrocarbon radlcal ammonium Salt of a copolymer of about 70% ethyl containing 1 to 8 carbon atoms or a polyalkenyl ether of ,acwlate and about methacrylic acid was blended 25 a polyhydric alcohol, said latex contaunng from about 0.1 with the latex to increase the overall carboxyl content of up to about 6% by welghb based on the total Welght the resulting butadiene binder latex. Papers saturated usof m f emulslfiel', selected P the group ing the procedure described in Example I, exposed to amcorislstmg 9 amomc and nomomc emuislfierst (2) monia for three minutes at 0 E and cured at acting the 1n1pregnated nonwoven web with ammonia or for five minutes had Wet breaking strengths of pounds/ 30 an aliphatic monoamme containing from 1 to 6 carbon inch internal bond strengths 1,92 ounces/inch atoms at a temperaturedess than 212 F. for about 1 when this Example is repeated with one part of a second to less than 80 mmutes; and (3) heating at a temperature between about 220 F. and 325 F. polymer of acrylic ac1d and 1% by weight of a polyallyl 2 Th f ether of sucrose having an average of 5.8 allyl groups per t e Process 0 Glam 1 Whel' @111 18 methyl methmolecule of sucrose, the resulting papers show increase acry a 3. The process of Claim 1 wherein m (c) the vm lrdene m internal bond strength. y

comonomer is selected from the group consisting of a EXAMPLES III-V vmyl aromatic, a vinyl or vinylidene halide, a vinyl ester, an u,p-unsaturated nitrile, and an unfit-unsaturated -P POIYITIer lfltlces Contalmng styfne 40 amide, and in (B) the unit-unsaturated carboxylic acid is and acr ylomtmle m terpolymerized were prepared using selected f the group consisting f acrylic and h. conventional emulsion polymerization techniques. The li acids latices were then used to saturate 10 mil flat paper and 4 The process f Claim 3 wherein the latex is main. tested for internal bond strengths and wet tensile strengthstained at a pH below 7.5 during impregnation, (2) i from The polymers of Examples and IV contained no 111- about 2 seconds to less than 5 minutes and (3) is between terpolymerized carboxyl-contammg monomers, therefore, 200 F. and 300 F. prior to use of these latices as binders, 2.5 parts of the 5. The process of Claim 4 wherein (B) is a copolymer carboxyl-containing copolymer described in Example II of the earboxylic acid and a polyalkenyl polyether of a was blended therewith. Test results are set forth in the polyhydric alcohol, said polyhydric alcohol containing Table with the internal bond strengths and wet tenslle about 4 carbon atoms and at least three hydroxyl groups strengths reported in ounces/inch and pounds/ inch respecand said polyether contains more than one alkenyl group tively. per molecule.

Paper saturated with Paper saturated latex plus 2.5 parts w1th latex copolymer thickener N 3min. NH 3min. NH; Example Polymer composition (parts) r p y determined exposurg %1 7% exposi fr h l g m 33butadi er w --liliiifiii%%i iitiiigirf""'"3::::::::::::::i::::: 13 22;? 1v as butadiene, 31 acrylonltrile, a N-methylol aerylamide.-- {Y 2g;';f%2gg?g &

V butadiene, 20 aerylonitrile, 20 methyl methaerylate, 5 {Wet tensile strength 3. 7 4, 7 1 0 17 6 methacryhe ac1d. Internal bond strength..- 3. 2 6. 1 18. 7 22. 3

The above Examples clearly point out the utility of the 6. The process of Claim 4 wherein (B) contains from Present invention The demonstrate that nonwoven about 15 to by weight of acrylic or methacrylic acid terials saturated wi y butadielle P with about 30 to 85% by weight of the ester of an ,5- mer latices exposed to ammoma have improved internal 7 olefinicauy unsaturated carboxylic acid bond strength and generally improved wet tensile strength. They also demonstrate that my process may be employed with butadiene hinder latices blended with carboxylcontaining copolymer latices to achieve the required carboxyl functionality. Oar-boxylated butadienestyrene and 7. The process of Claim 4 wherein (b) is about 20 to 45% by weight styrene or acrylonitrile, (B) contains from about 15 to 70% by weight of acrylic or methacrylic acid with about 30 to 85 by weight of the ester bntadiene-acryloni'trile latices, which may contain one or of an a,fi-olefinically unsaturated carboxylic acid.

8. The process of Claim 7 wherein the carboxylic acid is methacrylic acid in amount from about to 65% by weight and about to by weight of ester wherein the alkyl group contains 2 to 4 carbon atoms.

9. The processof Claim 8 wherein (a) is from about 50 to by weight butadiene, (b) is about 20 to 45% acrylonitrile, and there is up to about 40% by weight of vinylidene comonomer.

10. The process of Claim 9 wherein there is about 0.1 to 5% by weight of an acrylarnide, methacrylamide or a,;3-olefinically unsaturated N-alkylol amide of the formula wherein R is hydrogen or alkyl containing 1 to 4 carbon atoms and x is a number from 1 to 4.

12 11. The process of Claim 10 wherein the amide is N-methylol acrylamide.

References Cited UNITED STATES PATENTS 2,973,285 2/1961 Berke et a1 11762.2 2,983,623 5/1961 Coates 11762 3,085,897 4/1963 Priest et a1 11762.2 3,483,014 12/1969 Issacs et a1. 11762 HERBERT B. GUYNN, Primary Examiner US. Cl. X.R.

117106 R, A, UA, 161 UD; 16117O 

